1. Field of the Invention
The present invention is directed to a new class of allylic ethers. More specifically, the present invention is directed to a class of allylic ethers having carboxylate functionality, the alkyl 9-alkoxy-7-nonenoates. 2. Backoround of the Prior Art
Sebacic acid is a commercially important compound having particular application in its ester form as a plasticizer for polymers, especially polyvinyl chloride. This compound is relatively expensive because the only commercial method for its formation relies on a naturally occurring product, castor bean oil. Sebacic acid is obtained from said castor bean oil by extraction and oxidative cleavage. Although sebacic acid is expensive its unique flexibility and volatility properties support continued use of the compound as a plasticizer in polymeric applications. Obviously, the manufacture of this compound by synthetic means would be highly desirable.
It has now been suggested that a nonenoate having ether functionality at the end of the straight chain molecule opposite the ester functionality can be esterified to produce a diester which can be also easily synthesized to sebacic acid by hydrogenation and hydrolysis. The difficulty with this proposal is that a suitable nonenoate is not available in the prior art.
The compound methyl 9-methoxy-8-nonenoate is known in the art. This compound is disclosed in E.H. Pryde et al., Polymer Eng & Sci. 6, 60-65 (1966). Those skilled in the art are aware that this compound is a vinyl ether. The carbonylation reaction of a vinyl ether to form the ester, and thus produce a diester, is very difficult. Such reaction occurs at low rate and low selectivity and must be accompanied by extreme thermodynamic conditions, that is, at very high pressure and temperature. On the other hand, the equivalent carbonylation reaction of an allylic ether occurs at high rate and high selectivity, under moderate thermodynamic conditions, to easily produce the ester, that is, the diester when the starting reactant is an ester.
It is therefore not surprising that 9-methoxy-8-nonenoate, which, in E. H. Pryde et al., J. Org. Chem 29, 2083 (1964), is described as synthesizable from methyl 9,9-dimethoxynonanoate in a cracking reaction, although disclosed to have application as a plasticizer (E. H. Pryde et al., J.A.C.S. Div. of Org. Coatings, Plastics Chem Preprint 23 (2), 144 (1963)), is not suggested as an intermediate in the formation of a dicarboxylic acid.
The above remarks establish the need in the art for a new class of compounds which can be utilized as intermediates in a synthetic process for making sebacic acid.